Schistosomal glutathione-S-transferase (GST) is commonly used as a fusion partner when expressing proteins in E. coli (1). The GSTTag sequence has been reported to enhance the production and in some cases the solubility of its fusion partners. When expressed in a soluble, properly folded form, GSTTag fusion proteins can be purified with immobilized glutathione. Gentle elution is achieved with buffers containing reduced glutathione. Quantification of soluble GST fusions is also possible by assaying the transferase activity. In order to further enhance the utility of GST as a fusion tag, Novagen has designed two new multi-frame pET vectors, pET-41a-c(+) and pET-42a-c (+). In addition to featuring the powerful T7lac promoter, these vectors encode the GSTTag (220 aa), proteolytic sites, HisTag (6 aa) and STag (15 aa) sequences.

In contrast to other commercially available GST-fusion vectors, the Xa (IleGluGlyArg, pET-42 series) and enterokinase (AspAspAspAspLys, pET-41 series) proteolytic cleavage sites have been engineered to allow 100% complete removal of vector encoded sequences and the generation of native proteins with their authentic N-terminal residues.

The HisTag and STag sequences enable alternative protein detection and purification procedures to be performed; for example, when enhancing purity with a separate purification method, or when purifying under denaturing conditions.

1. Smith, D.B. and Johnson, K.S. (1988) Gene 67, 3140.